Sliding contact



p 1, 1970 J. M. RAMRATH 3,526,736

SLIDING CONTACT Filed Dec. 19, 1968 United States Patent 3,526,736SLIDING CONTACT Joseph M. Ramrath, Mattapan, Mass., assignor t0 Allis-Chalmers Manufacturing Company, Milwaukee, Wis. Filed Dec. 19, 1968,Ser. No. 785,227 Int. Cl. H01h 1/34; H01n 1/54 US. Cl. 200-166 6 ClaimsABSTRACT OF THE DISCLOSURE A sliding contact for engagement with acylindrical bayonet type contact having a central opening and aplurality of pivotal contact fingers radially disposed around theopening so that one end of each contact finger can make slidingengagement with the side of the bayonet contact when the latter entersthe opening. Current flow, from the bayonet contact to the slidingcontact, follows a looped path and generates a magnetic field which aidsin forcing the contact fingers against the bayonet contact.

SUMMARY OF THE INVENTION This invention relates generally to electricalcontacts. More particularly, it relates to sliding contacts which engagewith relatively movable bayonet contacts.

Sliding contacts employ a plurality of contact fingers, either linearlyor radially disposed, which engage a relatively movable bayonet contact.Sliding contacts presently available are satisfactory for their intendedpurposes but could be improved on. For example, in one type of slidingcontact, the individual spring biased contact fingers or segments areradially disposed around a bayonet contact but tend to move laterallyout of position when subjected to high peak currents and attendantelectromagnetic forces. Furthermore, these electromagnetic forces tendto lift the contact fingers off of the bayonet contact thereby causingsevere burning and scoring at the lift-off points. These electromagneticforces also cause lateral shifting of the contact fingers so that theytouch each other thereby causing irregularly shaped current paths whichcause additional burning and scoring between the contact fingers.Accordingly, it is desirable to provide an improved sliding contactwhich overcomes the aforesaid disadvantages and has other advantages.

In accordance with the present invention, there is provided a slidingcontact for engagement with a relatively movable bayonet contact. Thesliding contact comprises an electrically conductive base member havingan opening for accommodating the bayonet contact. The base is providedwith an electrically conductive flange adjacent said opening and theflange is provided with a groove on the side thereof away from theopening. A plurality of C-shaped contact fingers or segments arearranged on the base near the opening. One end of each contact fingerpivotably engages the groove in the flange on the base member. The otherend of each contact finger is adapted to pivot toward the opening forengagement with the bayonet contact. Insulating means are provided onthe base to physically support the contact fingers, to prevent directelectrical contact between them, and to limit pivotal movement of thecontact fingers. Biasing springs are disposed between the insulatingmeans and the contact fingers for biasing the contact fingers toward theopening. Each contact finger, the flange and the base are shaped3,526,736 Patented Sept. 1, 1970 so as to provide a looped path forcurrent flowing from the bayonet contact, through the contact finger,flange and the base. The electromagnetic forces associated with thelooped current path tend to move each contact finger tightly against thebayonet contact.

OBJECTS It is an object of the present invention to provide improvedsliding contacts having contact fingers which are prevented from makingdirect electrical contact with each other.

Another object is to provide sliding contacts of the aforesaid characterhaving contact fingers which are individually supported and electricallyinsulated from each other.

Another object is to provide sliding contacts of the aforesaid characterwherein each contact finger is pivotably mounted on a flange on the baseand wherein each contact finger, the flange, and the base form a currentloop which generates an electromagnetic field which causes increasedpressure between the contact finger and the flange and the bayonetcontact as current flow increases.

Another object is to provide sliding contacts of the aforesaid characterwherein current flow from the bayonet contact radiates outward throughindividual contact fingers in straight line paths with respect to theaxis of the bayonet contact.

Another object is to provide sliding contacts of the aforesaid characterwhich are relatively economical to manufacture and assemble and whichhave greater current carrying ability than known types of slidingcontacts of comparable size.

Other objects and advantages of the invention will hereinafter appear.

DRAWINGS The accompanying drawing illustrates a preferred embodiment ofthe invention, but it is to be understood that the embodimentillustrated is susceptible of modifications with respect to detailsthereof without departing from the scope of the appended claims.

In the drawing:

FIG. 1 is a plan view with portions broken away of a sliding contact inaccordance with the present invention; and

FIG. 2 is a cross sectional view taken along line -IIII of FIG. 1.

DESCRIPTION OF THE INVENTION Referring to FIGS. 1 and 2 of the drawing,the numeral 10 designates a sliding contact in accordance with thepresent invention. Sliding contact 10 is adapted to cooperate with anelectrically conductive cylindrical bayonet contact 12. It is to beunderstood that the contacts 10 and 12 are relatively movable withrespect to each other and either could be the stationary or movablecontact in a piece of electrical equipment. However, in the embodimentshown, sliding contact 10 is the fixed or stationary contact and bayonetcontact 12 is the movable contact. Sliding contact 10 comprises anelectrically conductive base member 14 which is provided with a centralopening 16 for accommodating bayonet contact 12. Base member 14 isadapted for electrical and mechanical connection to an electricallyconductive member 18 which is to be understood to be part of a piece ofelectrical equipment and which serves as a physical support for slidingcontact and as an electrical connection thereto. Base member 14 isprovided with a circular depression which is concentric with opening 16and which is bonded on each side by cylindrical flanges 21 and 22. Thedepression 20 further accommodates components hereinafter described.Preferably, depression 20 in base 14 is deeper nearer the inside thereofto afford clearance space as at 26 for movement of the contact fingers28. Cylindrical flange 22 is disposed around and adjacent opening 16.Flange 22 is provided on the side facing away from opening 16 with acircular groove 24 which as FIG. 2 shows has a V-shaped cross section.However, groove 24 could have a curved cross sectional configuration.

Sliding contact 10 further comprises a plurality of electricallyconductive contact fingers or segments 28 which are disposed on base 14and adapted to cooperate with bayonet contact 12. In the embodimentshown,

sixteen radially disposed contact fingers 28 are provided but a greateror lesser number could be employed. Since all contact fingers 28 areidentical, only one of them will hereinafter be described in detail.

As FIG. 2 shows, a contact finger 28 has a substantially C-shaped orU-shaped configuration. One end 30 of contact finger 28 is rounded andis disposed in groove 24 in flange 22 of base 14 so as to be pivotabletherein and to make electrical contact with the flange. The other end 32of contact finger 28 is also rounded and is adapted to make slidingcontact with the side surface of bayonet contact 12, as hereinafterexplained.

Means are provided on base 14 to physically support the contact fingers28 in radial arrangement, to physically separate and electricallyinsulate each contact finger from another, and to control or limitpivotal move- I merit of the contact fingers. Such means comprise firstand second insulating plates 34 and 36, nespectively. As FIG. 1 shows,insulating plate 34 is provided with slots or notches 38 and each notchaccommodates a contact finger 28. Insulating plate 36 is also providedwith similar notches 40. The insulating segments 41 and 43 between thenotches 38 and 40 in the plates 34 and 36, respectively, limit lateralmovement of any contact finger 28 disposed therebetween and also preventany contact finger 28 from making direct physical or electrical contactwith any other contact finger. An insulating member 42 having notches 44is disposed between the plates 34 and 36 and serves to space them part,and cooperates therewith to define cavities which serve as springretaining means. Each notch 44 in member 42 accommodates a biasingspring 46 which bears against the rear of the associated contact finger28 and tends to bias its end 32 toward opening 16 in base 14 and its end30 against flange 22. Under the action of its biasing spring 46, eachcontact finger 28 tends to pivot clockwise (with respect to FIG. 2) intotight engagement with bayonet contact 12, if the latter is disposed inopening 16. However, such pivotal travel of contact finger 28 is limitedby means such as an insulating plate 50 which overlies insulating plate34. The insulating plates 34, 42, 36 and 50 are rigidly secured withrespect to each other and with respect to base 14 by means of aplurality of bolts 52 which extend through appropriate holes in theinsulating plates and into threaded holes (not shown) in base 14.

Sliding contact 10 operates as follows. Assume first that bayonetcontact 12 is withdrawn from opening 16. Under such circumstances eachbiasing spring 46 forces its associated contact finger 28 to pivotclockwise with respect to FIG. 2 as far as insulating plate 50 willpermit. Thus, a portion of end 32 of each of the contact fingers 28extend into opening 16 in base 14 and into the path that bayonet contact12 will eventually traverse. When bayonet contact 12 enters opening 16in base 14 axially, it engages the ends 32 of all of the contact fingers28 and forces them back against the bias of their associated springs 46thereby assuring that a good electrical connection exists between theside surface of bayonet contact 12 and contact fingers 28. Currentflowing from bayonet contact 12, through each contact finger 28, throughflange 22, through base 14 and through member 18 follows a looped path,as shown by an arrow 54 in FIG. 2. The current path depicted by thearrow 54 is looped and generates an electromagnetic field which forcesits contact finger 28 to move in a clockwise direction (with respect toFIG. 2). Thus, the action of the biasing springs 46 and the action ofthe electromagnetic forces cause all contact fingers 28 to tightlyengage bayonet contact 12. As current flow increases, the magneticforces increase, thus insuring an even tighter electrical connection Theembodiments of the invention in which an exclusive property or privilegeis claimed are defined as follows:

1. In a sliding contact for cooperation with a bayonet contact,

an electrically conductive base having an edge past which said bayonetcontact is adapted to move, said base having a flange adjacent said edgeand said flange having a groove therein on the side away from said edge,at least one contact finger, one end of said contact finger disposed insaid groove and pivotable therein and the other-end of said contactfinger extending over said flange and toward said edge and adapted toengage said bayonet contact when the latter is disposed adjacent saidedge, insulating means on said base for supporting said contact fingerand for limiting pivotal movement thereof, and biasing means disposed ina recess in said insulating means between said insulating means and saidcontact finger for biasing said contact finger in said groove and forpivoting it toward said edge, said base, said flange and said contactfinger forming a current path which, during current flow there through,generates an electromagnetic field which forces said contact fingeragainst said bayonet con tact and said flange.

2. A sliding contact according to claim 1 wherein said insulating meansis provided with a slot wherein said contact finger is disposed, andbeing further provided with a recess wherein said biasing means in theform of a spring is located, said insulating means having a portionoverlying said slot for limiting pivotal movement of said contactfinger.

3. A sliding contact according to claim 2 wherein said insulating meanscomprises a pair of contact supporting members, a spring retainingmember disposed between said contact supporting members, and a stopmember overlying one of said contact supporting members to limit pivotalmovement of said contact finger, said contact supporting members beingslotted to accommodate said contact finger and prevent substantiallateral movement thereof, and said spring retaining memher being slottedto provide a recess to accommodate said spring.

4. A sliding contact according to claim 2 wherein said base has anopening therethrough which defines said edge and wherein a plurality ofcontact fingers, slots,

and recesses are provided, at least some of said contact fingers, slotsand recesses being disposed on different sides of said opening.

5. A sliding contact according to claim 4 wherein said contact fingers,slots and recesses are radially disposed.

6. A sliding contact according to claim 3 comprising a plurality ofcontact fingers, slots and recesses disposed in radial arrangement, andwherein said contact sup porting members and said spring retainingmembers are 5 6 provided with central openings from which the slots3,137,778 6/ 1964 Barr 200-166 XR radiate. 3,328,550 6/1967 Miller200166 References Cited 3,381,105 4/ 1968 Morte-nson 200-166 XR UNITEDSTATES PATENTS HERMAN 0. JONES, Primary Examiner 2,180,155 11/1939Leopold 200--166 5 2,751,471 6/1956 Wills 200-166 US. Cl. X.R. 3,127,4923/1964 Date 200-166 200-170

